Abstract. The MHD drift ballooning mode (DBM) instability near the inner edge of the near-Earth plasma sheet is studied by using both the one-fluid generalized progressing wave expansion method and the two-fluid approach. It is found that in the frame of reference •t rest relative to the bulk plasma the DBM may become a purely growing mode in two distinct circumstances, which, for convenience, are called the DBM1 and DBM2, respectively. The/• threshold for the DBM1 is identical with that derived by Ohtani and Tamao [1993] and Southwood and Kivelson [1987], while the criterion of the DBM2 covers that of Miura et al. [1989].Comparisons of the theory with GEOS 2 data show that the DBM2 is more easily excited in the late substorm growth phase. There is considerable evidence that the D BM is generated at expansion onsets. The characteristic features of magnetic field dipolarization can be interpreted in terms of the development of the DBM. The extremely thin current sheet cases should be studied with approaches other than those used in this work.
Introduction Study of MHD waves and instabilities in the near-
Abstract. The drift ballooning mode (DBM) instability near the inner edge of the plasma sheet (IEPS) is studied further by including a nonstationary earthward flow and flow shear in the analysis. Both equatorial and off-equatorial regions are considered. It is found that the presence of a decelerated earthward flow destabilizes both the M_ and M+ branches of the DBM in a large portion of the current sheet near the IEPS and substantially increases the growth rate of the instability. The flow shear in the prelnidnight sector causes the conventional ballooning mode to weakly subside, while it slightly enhances the growth rate for the Alfv6nic ballooning mode.The combination of the earthward flow and flow shear makes both the Alfv6nic ballooning mode and conventional ballooning mode grow much faster than they would without the flow, giving rise to coupled Alfv6nic slow magnetosonic waves, field-a, ligned currents, and the formation of a current wedge. A synthesis of tail reconnection and cross-tail current disruption scenarios is proposed for the substorm global initiation process: When the fast flow produced by magnetic reconnection in the midtail a. bruptly decelerates at the IEPS, it compresses the plasma populations earthward of the front, transports momentum to them, and pushes them farther earthward. This creates the configuration instability in a large portion of the inner tail magnetic field lines on both the tailward side and earthward side of the braking point. As soon as the ionospheric conductance increases over a threshold level, the auroral electrojet is greatly intensified, which leads to the formation of the substorm current wedge and dipolarization of the magnetic field. This substorm paradigm combines the near-Earth neutral line and near-Earth current disruption scenarios for the initiation of substorms and may also synthesize dynamical processes in the magnetosphere-ionosphere coupling and field line resonance during the substorm onset. We intend to use this global model to explain substorm expansion onsets occurring under the southward interplanetary magnetic field condition.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.